Interspecific comparison of the flight performance between sparrowhawks and common buzzards migrating at the Falsterbo peninsula: A radar study

In order to compare the two species’ flight performance over the exposed and windy Falsterbo Peninsula, where
thermal conditions seldomly are very favorable, we used tracking radar to study flight parameters of sparrowhawks Accipiter nisus
and common buzzards Buteo buteo during autumn migration. The results showed a clear difference between sparrowhawks
and common buzzards in their flight altitudes and speeds, and in the wind conditions they encountered. Common buzzards had
higher flight altitudes and were more selective of wind. Flight altitude was negatively related to the wind speed, which was most
pronounced for common buzzards. Sparrowhawks had higher mean air- and cross-country speeds than common buzzards. Airspeed
was negatively related, whereas ground and cross-country speeds were positively related to the tailwind component for
both raptors. The differences between sparrowhawks and buzzards could to a large degree be explained by a larger dependence on
thermal soaring among the common buzzards; a strategy associated with selectivity for favourable thermal and wind conditions
during migratory flight. An additional important explanation for the interspecific differences was the habit of the sparrowhawks
to combine migratory flight with hunting for prey, which makes it prone to fly at lower altitudes and use flapping flight to a much
larger degree than common buzzards which do not forage during their migratory passage of the Falsterbo Peninsula.